In a collaborative effort with the Washington Regional Primate Research Center (WRPRC) we have discovered three gammaherpesviruses related to Kaposi's Sarcoma-associated herpesvirus (KSHV) in RF lesions of two macaque species, M. nemestrina (Mn) and M. mulatta (Mm). RF is an aggressively proliferating tumor which is rapidly fatal, and has morphological similarities to KS. Recent studies suggest that KSHV plays an etiological role in the pathogenesis of KS. Two of the new macaque viruses, RFHVMn and RFHVMm are closely related to each other and to KSHV. The third, nemestrina rhadinovirus (NRV), is closely related to another gammaherpesvirus from M. mulatta, called rhesus rhadinovirus (RRV). We group these viruses in a new gamma3 genus of herpesviruses with a gamma3A subgroup consisting of KSHV, RFHVMn and RFHVMm and a gamma3B subgroup consisting of NRV and RRV. With the discovery of NRV, we have now determined that all the macaques studied with RF tumors were infected with either a gamma3A or gamma3B virus, or were co- infected with viruses from both groups. These results support our hypothesis that KSHV-like herpesviruses of macaques play an etiological role in the pathogenesis of RF and that SRV-2 associated RF is a relevant animal model for the study of AIDS- KS. We are currently characterizing the genomes of RFHVMn/Mm and NRV in order to compare them to KSHV and RRV. We are especially interested in viral homologs of growth regulatory genes which appear important for viral pathogenicity. To study the biological and pathological differences between the gamma3A and gamma3B macaque viruses, we are examining cellular tropism, gene activation and interactions with SRV-2. Our long term goal is to determine the contributions and interactions of these types of herpesviruses with retroviruses and endogenous cellular factors in the induction and progression of KS-like malignancies. For this application, we propose the following specific aims: 1) Determine the genomic organization of the macaque gamma3A herpesvirus, RFHVMn, 2) Identify and characterize RFHVMn homologs of cellular genes involved in growth regulation and cellular transformation, 3) Determine the cellular tropism and replicative state of macaque gamma3A and gamma3B KSHV-like herpesviruses and SRV-2 in RF tumors and non-tumor tissue from infected macaques, 4) Establish the baseline parameters of the infectious cycle of the macaque gamma3A and gamma3B KSHV-like herpesviruses.